1. Field of the Invention
The present invention relates generally to implantable devices. More specifically, the present invention relates to a method of optimizing storage of electrophysiological data in an implantable cardiac device.
2. Background Art
The heart is a series of pumps that are carefully controlled by an electrical system. This electrical system attempts to regulate the heart rate between 60 and 100 beats per minute (bpm). Abnormally fast heart rates are called tachycardias. As used herein, the term tachycardia means a heartbeat at a rate which is abnormally high and accordingly considered to be dangerous if permitted to continue, or any arrhythmia involving recognizable heartbeat patterns containing repetitions which are in excess of a periodic heartbeat within a safe range. When the ventricular chambers beat too quickly, the arrhythmia (i.e., unusual heart rhythm) is known as ventricular tachycardia (VT). When VT occurs, the ventricles may not be able to fill with enough blood to supply the body with the oxygen rich blood that it needs. Symptoms of VT include feeling faint, sometimes passing out, dizziness, or a pounding in the chest.
Ventricular fibrillation (VF) is a very fast and irregular heartbeat that is caused by abnormal impulses coming from several areas of the heart. These abnormal impulses take over the natural pacemaker function of the sinoatrial (SA) node. The heartbeat is so fast and irregular that the heart does not pump enough blood to the brain and body tissue, which may cause unconsciousness, or death.
Arrhythmias in the heart have typically been treated using electro-pacing or shock therapy. For example, when a patient's heart is found to be in VF, a jolting electrical pulse, or shock pulse, is delivered to the patient in order to reactivate the electrical signals throughout the heart. The shock pulse may be administered via external defibrillators, or via implantable cardioverter defibrillators (ICDs) configured to deliver such a shock.
ICDs, and other implantable cardiac devices, usually have memory storage units to record and store electrophysiological data from the patient. Specifically, data representing the time immediately before, during, and after an arrhythmia is stored for later analysis. Typically, devices use various ultrabreak (polynomial based) compression algorithms to store the data. Compression algorithms allow storage of the data while effectively using minimum amounts of memory. However, compression algorithms require a lot of processing power from the device's battery in order to compress the data, hence reducing the longevity of the device. Also, compression algorithms often take a long time to compress the data, which introduces interaction problems with other critical processes in the device. Compression algorithms are also not effective for compressing noisy and high frequency signals.
What is needed is a method of optimizing storage of electrophysiological data in the memory unit of an implantable device.